In current air traffic control practices, controllers allocate speeds to aircraft, or make them execute lateral manoeuvres, to ensure efficient sequencing of the aircraft in the terminal control zones. Various tools have been devised to aid the controller in this task. The aircraft's flight predictions make it possible to estimate its flight time and its time of arrival at certain characteristic points of the approach. Tools such as an Arrival MANager AMAN then make it possible to display the arrival sequence of the various aircraft, and to identify for each a time to be lost (“Time To Loose”) or to be gained (“Time To Gain”) in order to establish a runway sequencing of the aircraft which satisfies the required rate, while maintaining the separation necessary for flight safety. The choice of the speed setpoint or lateral manoeuvre setpoint is assessed by the controller according to the timespan to be gained or lost, by taking into account the surrounding traffic. The information regarding vertical prediction of the aircraft, available through the ADS-C (Automatic Dependent Surveillance Broadcast) protocol in the form of EPP (Extended Projected Profile), is today not taken into account in determining the lateral or speed setpoints.
Current aircraft are capable of determining a descent profile optimized according to an economic criterion, often a cost index, achieving a compromise between fuel consumption and flight times, sometimes summarized in the form of a performance criterion. The descent speed profile, as well as the descent start point, are determined so as to maximize the use of a minimum thrust in the course of descent, while satisfying the altitude and speed constraints required by the flight plan. These constraints may arise from the procedures defined in a navigation database and inserted into the flight plan, or may have been input by the pilot, on request or otherwise of the ground operator.
When an arrival time constraint is required (also called RTA (“Required Time of Arrival”) or CTA/CTO (“Constrained Time of Arrival/Overfly”)), the embedded Flight Management System FMS may compute a new speed profile, and the associated descent profile, making it possible to satisfy the temporal constraint. The RTA speed computation profiles can be ensured in several ways, either by searching for a cost index which satisfies the constraint as described in patent application U.S. Pat. No. 8,744,768, or according to more elaborate speed strategies, for example by using the temporal profiles corresponding respectively to a flight at minimum, maximum, or economic speed, as described in patent application U.S. Pat. No. 8,332,145. It is also possible to automatically compute a lateral manoeuvre ensuring the desired arrival time as described in patent application U.S. Pat. No. 8,457,872. The criterion for determining these manoeuvres remains the time constraint, without taking energy management into account.
Within the framework of inter-aircraft synchronization operations of ASAS (“Airborne Separation Assistance System”) or FIM (“Flight deck based Interval Management”) type, using the data exchanged between aeroplanes by the ADS-B protocol, lateral manoeuvres and speed manoeuvres have been devised to acquire and then remain at a temporal or spatial spacing behind another aircraft. A lateral manoeuvre consists in determining, on the current route or along the current heading, a point for turning towards a specified point, making it possible to acquire the required spacing as described in applications U.S. Pat. No. 8,386,158, U.S. Pat. No. 8,078,341 or U.S. Pat. No. 8,862,373. Next, a speed adjustment is applied so as to refine and maintain the specified spacing. But the turning point, like the speed setpoint, are established so as to obtain the required spacing, without taking into account the impact on the energy or the descent capability of the aircraft.
Moreover, methods have been defined for automatically ensuring the lateral and vertical rejoining of a flight plan and of a reference descent profile as described in patent application U.S. Pat. No. 8,515,598, optionally while maximizing the use of the minimum thrust as described in application U.S. Pat. No. 9,188,978. During these lateral and vertical capture manoeuvres, the energy of the aeroplane can be taken into account in order to adjust the vertical profile, and the required distance in order to ensure stabilization can be evaluated. In particular, the trajectory can be modified and lengthened in order to ensure sufficient length for stabilization of the aircraft before landing. However, these methods do not take into account an optional time constraint to achieve the best compromise between speed and length of trajectory, in such a way as to maintain a descent hold under minimum thrust.
Taking a time constraint into account in the computation of an energy-optimized descent profile has also been proposed in patent application U.S. Pat. No. 9,026,275 but acting on the altitude, speed, thrust parameters over a predetermined lateral trajectory, without using the lateral modification of the trajectory as optimization degree of freedom.
Finally, patent application US 20160063867, published on 3 Mar. 2016, describes an adjustment of the speed and of the lateral trajectory, in the presence of a fixed temporal constraint on a target rejoining point. The method described consists in monitoring the energy and the transit time at a downstream point of the descent, in such a way as to ensure compliance with the flight plan. The energy recovery system, described by this document, implements a computation method which identifies the necessary adjustments of trajectory control parameters so as to force the aircraft to follow profiles in respect of energy recovery and of time at the arrival target point using a minimum lengthening of the lateral trajectory. The method described can lead to adjustments of the speed and of the lateral trajectory but also includes the possibility of additional thrust or drag. The objective claimed in this document is to secure energy compliance by priority, and subsidiarily if possible, compliance with the required flight time, without systematically seeking economic optimization. Furthermore, the method describes neither the manner of computing the vertical profile, nor the way in which account is taken of the effects of the wind and/or of the lateral trajectory on this profile.
This method does not therefore specify how, in the presence of an appreciable modification of the arrival time scheduled in the flight time, a lateral manoeuvre can be devised so as to comply with the new arrival time while achieving the most economically efficient compromise in terms of fuel consumption.
A first technical problem is to provide a method for determining a minimum-thrust descent and rejoining profile in respect of a target point by an aircraft in which the fuel consumption along the profile is minimized without energy surfeit of the aircraft and while complying with the fixed arrival time constraint at the target descent and rejoining point.
A second technical problem is to provide a method for determining a minimum-thrust descent and rejoining profile, which solves the first technical problem and is simple to implement.